rpcrt4: Fix copying too much data from the buffer by not taking into account the fact that auth_pad_len has been included in the fragment length.

Protect LPGUID typedef by __LPGUID_DEFINED__ being defined.

Protect LPCLSID and LPFMTID typedefs, IsEqualGUID, IsEqualIID,
IsEqualCLSID, IID_NULL, CLSID_NULL and FMTID_NULL defines by
__IID_DEFINED__ being defined.

PSWIZB_DISABLEDFINISH, followed by another one without those flags
should show the next button again and hide the finish button.